1. Field of the Invention
The present invention relates to a light-guide coupler. More particularly, the present invention relates to a slim light-guide coupler for modulating angular and spatial distributions of a light source.
2. Description of the Prior Art
To provide collimating light, conventional techniques use a compound parabolic collector (CPC) to transform the light from Lambertian distribution to collimating distribution. The light-angle distribution relationship of a CPC complies with the following equation:
                                          A            1                                A            2                          =                              (                                                            n                  2                                ⁢                                  sin                  ⁡                                      (                                          θ                      2                                        )                                                                                                n                  1                                ⁢                                  sin                  ⁡                                      (                                          θ                      1                                        )                                                                        )                    2                                    (        1        )            
A1 and A2 respectively denote the section area of the input and output. θ1 and θ2 respectively denote the angle distribution of input and output. n1 and n2 are the refractive index of the respective medium.
Considering a two-dimension CPC, the aforesaid equation (1) can be rewritten as:
                                          W            1                                W            2                          =                              (                                                            n                  2                                ⁢                                  sin                  ⁡                                      (                                          θ                      2                                        )                                                                                                n                  1                                ⁢                                  sin                  ⁡                                      (                                          θ                      1                                        )                                                                        )                    2                                    (        2        )            
W1 and W2 denote the width of CPC input and CPC output. According to equations (1) and (2), the output area is greater than the input area, and the CPC have better transferring efficiency between scattering light and collimating light. However, the greater size of the output means that the CPC will have a wider and thicker transmission body size.
Thus, providing a light-guide coupler having a thinner transmission body and greater transferring efficiency is a technical issue which needs to be solved in the technical field.